A leak in the door seal, ie the door does not always seal correctly. Leave
it open a crack and see what occurs, I did theirs accidentally, and the
result was ice inside and of course around where the leak was.
Bah humbug. Does it have a fan that might occasionally jam up?
Brian

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The Sofa of Brian Gaff...

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"NY" wrote in message
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We have a supposedly frost-free freezer which mostly works as designed:
the cooling fins on the heat-exchanger remain clear of ice. But several
times over the last year, we have found the reported temperature
increasing and a lot of ice around the heat-exchanger, so we have to take
everything out (thank goodness for a spare freezer) and defrost/re-freeze.

There is no sign of obvious blockage in the pipe that drains the
heat-exchanger to a tray above the motor/compressor.

It doesn't seem to happen at any particular time of year, and as far as we
are aware, we don't store more/less food in there or open the door more at
some times of year than another.

I'm intrigued what could cause a freezer to keep itself frost-free for
several months (with no visible gradual build-op of ice) and then suddenly
ice up.